Brake signal failure detecting system and method for automatic transmission

Abstract: A failure detecting system for an automatic transmission of a vehicle having a vehicle speed sensor mounted on said vehicle for sensing a vehicle speed and for generating a vehicle speed signal indicative thereof, comprising: a brake switch mounted on said vehicle for detecting whether a brake system is operated or not and for generating a brake signal indicative thereof; brake signal detecting means (1004) for detecting a brake signal when said brake is turned on; shift signal generating means for generating a shift signal so as to instruct an appropriate gear position to said automatic transmission; and transmission control prohibiting means (1010) for prohibiting a transmission control based on said brake signal, when said shift signal from said shift signal generating means indicate a change from a parking (P) range to a reverse (R) range, and when a number of times (1008) of how often said brake signal which ought to be detected has not been detected reaches a predetermined number of times (N); in a second embodiment the transmission control prohibiting means are responsive to said vehicle speed signal and said brake signal, for prohibiting control of said automatic transmission based on said brake signal when a first predetermined number (N) of times is counted while said vehicle speed decreases from a predetermined speed (30km/hr) to a zero speed without detecting operation of said brake system, thereby indicating a failure in said brake system.

Description: The present invention relates to a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed, a cruise control signal, a brake signal from a brake switch or a shift range switch operation signal from a shift range switch as one of control signals to control the automatic transmission. An automatic transmission AT is fundamentally controlled to be shifted by regulating depression of an accelerator pedal and a traveling speed of a vehicle. Accordingly, in case where the vehicle travels in a drive (D) range, reduction gears can be shifted by positively depressing or releasing the accelerator pedal. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selectively controlled from a vehicle speed at that time and a throttle opening according to a shift map storing a predetermined shift schedule as shown in Fig. 6. As a lockup function of an automatic transmission a lockup clutch is engaged when a vehicle speed becomes higher than a predetermined value in a certain gear position such as, for example, in a third gear or an overdrive (fourth gear), to directly couple an output shaft of a torque converter to an output shaft of an engine. In other cases, the lockup clutch is released to connect the input shaft of the torque converter to the output shaft of the engine. The lockup is released to utilize a function of the torque converter thereby to achieve smooth starting, smooth accelerating or smooth speed shifting without engine knocking or stop at the time of starting, abruptly accelerating, speed shifting the vehicle. However, in a state that a load is low and an engine rotational speed is high, the torque converter is locked up thereby to prevent loss of power due to a slip of the torque converter and hence to prevent an increase in fuel consumption. A cruise control unit so controls an opening of a throttle valve as to maintain a certain vehicle speed set by a driver as a desired traveling speed thereby controlling in response to a road state. As the typical automatic transmission control to execute as described above, JP-U-63-115558 discloses an internal combustion engine with an abnormality detector for judging an abnormality based on a rotational speed signal from a rotation detector for electrically detecting a rotational speed of the internal combustion engine and a fuel amount signal from a fuel amount detector for detecting a fuel supply amount to the internal combustion engine. In the above-described internal combustion engine with the abnormality detector, it is determined that an engine rotational speed signal line is on when an engine rotational speed is smaller than a predetermined value at a certain vehicle speed or more. However, even if an engine stop occurs at a certain vehicle speed or more, it is erroneously detected that the failure occurs at the engine rotational speed signal line. In such a case, it becomes impossible to detect a failure of an ignition pulse generating an engine rotational speed detection signal to be supplied to the engine rotational speed signal line. Furthermore, there are disadvantages that the automatic transmission control based on the engine rotational speed such as, for example, a gear shift control, a lockup control, a line pressure control can not be appropriately controlled. As the typical automatic transmission control to execute as described above, JP-U-63-137038 discloses an automatic transmission controller in which hunting of the vehicle speed due to a gear shifting during a cruise control traveling is prevented and a fail-safe control is performed when an abnormality of an automatic transmission occurs. More specifically, the automatic transmission controller additionally provides a memory map storing a shift schedule for controlling the automatic transmission in response to a cruise control signal supplied from a cruise controller, in which map a hysteresis width is so set as to reduce the number of repetitions of down and up shifting. In this case, since the number of times of gear shifting during the cruise control is reduced, hunching of the vehicle speed due to the gear shifting can be prevented, and a riding comfort can be improved. In the conventional automatic transmission controller as described above, a vehicle can be traveled smoothly without shock in the case of shifting gear during the cruise control, but it does not have a fail-safe function in case where the cruise control signal is, for example, erroneously generated even though the cruise control is not performed by the cruise controller. Usually, the automatic transmission controller functions as a gear shifting control, a lockup control, an overrunning clutch control (namely, engine brake control), etc. Therefore, if a fail-safe function is not provided, these functions are erroneously operated when a cruise control signal is erroneously generated. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selected based on a vehicle speed and a throttle opening at that time, from a shift schedule map storing a predetermined shift schedule as shown in Fig. 6. Further, in such an automatic transmission control, detection signals from various detecting sensors are input to a controller to perform a lockup control, an overrunning clutch control, a line pressure control, an auto-pattern select control, a gear shift timing control, a transfer clutch control of four-wheel drive as well as the above-described gear shift control. JP-A-1-145234 discloses a cruise control of a vehicle using a brake switch signal. Furthermore, JP-A-63-34349 discloses a method for detecting a trouble of a gear position switch. That is, if a gear position switch does not generate an ON signal when a predetermined time is elapsed after a gear shifting is performed, it is returned to a position before the gear changing, and when the same operation as above is conducted predetermined times or more, the switch is decided to be a trouble. However, in the above-described conventional method for detecting the trouble of the gear position switch, in case where the ON signal is not generated from the gear position switch, the gear is returned to the position before the gear shifting, and when the same operation as above is again conducted predetermined times or more, the switch is decided to be the trouble. Therefore, in the case of the trouble, it merely controls to return the position of the switch to the position before the gear shifting, an accurate automatic transmission control responsive to various traveling states of the vehicle is impossible. US-A-4 750 385 relates to an automatic transmission control apparatus comprising the features of the preamble of claims 1, 4, 5 and 8. The abrupt loss of the vehicle speed is detected for transmission control purposes when the brake is under man operating conditions. An object of the present invention is to provide a failure detecting system for a brake switch connected to a controller for an automatic transmission of a vehicle which can reliably detect a failure of a brake responsive to various running states thereby to appropriately control an operation of an automatic transmission control based on a brake switch signal. This object is achieved with the features of the claims. According to the failure detecting system for the brake switch of the present invention, the automatic transmission control of the automatic transmission AT is prohibited in case where one of the following conditions is satisfied. More specifically, (1) When a brake ON signal is not detected when the vehicle speed is decelerated until a vehicle is stopped, and when this phenomenon occurs continuously predetermined times. (2) When a deceleration of the vehicle speed is larger than a predetermined value, the brake ON signal is not detected, and when this phenomenon occurs continuously predetermined times. (3) In case where a vehicle speed is larger than a certain value, and the paragraph (2) is satisfied. (4) In a vehicle having a shift locking mechanism, when a R range is selected from a P range, absence of the brake ON signal continuously occurs predetermined times. In case where any of the above conditions (1) to (4) is satisfied, it is determined that a failure occurs on the brake switch signal, the automatic transmission control in response to the brake switch signal is prohibited. However, a normal state is recovered when the brake ON signal is detected after one of the the above-described conditions is satisfied. The nature, utility, and further features of this invention will be understood from the following detailed description with respect to preferred embodiments of the invention by referring the accompanying drawings, briefly described below. In the accompanying drawings: Fig. 1 is a block diagram showing a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed according to an embodiment of the present invention; Fig. 2 is a flow chart for explaining an example of the operation of the failure detecting system for a brake switch according to Fig. 1; Fig. 3 is a flow chart for explaining an example of the operation of the failure detecting system for a brake switch according to Fig. 1; Fig. 4 is a flowchart for explaining an example of the operation of the failure detecting system for a brake switch according to Fig. 1; Fig. 5 is a flow chart for explaining an example of the operation of the failure detecting system for a brake switch according to Fig. 1; Fig. 6 is a view showing a shift schedule stored in a gear shift map for a conventional automatic transmission control; The embodiment of the present invention will be explained with reference to accompanying drawings. Fig. 1 shows a control system according to an embodiment of a failure detecting system for an automatic transmission of a vehicle of the present invention. The control system employs an engine rotational speed as one of input signals to control the automatic transmission. A failure is detected on the engine rotational speed when conditions to be described later are satisfied. When the failure is detected, a transmission control based on the engine rotational speed is prohibited, and a state before the failure is detected is maintained. The controls based on the engine rotational speed includes, for example, a gear shift control, a lockup control, and a line pressure control. A throttle opening detection signal from a throttle sensor 11 and an ATF oil temperature detection signal from an ATF temperature sensor 12 are input to an input interface circuit 21 of an electronic control unit (ECU) 20 of the control system. The throttle opening detection signal from the throttle sensor 11 is used to determine a gear shifting point, a line pressure in a control circuit of the automatic transmission and a lockup vehicle speed for the lockup. The ATF oil temperature detection signal from the ATF temperature sensor 12 is used to prohibit lockup at the time of a low temperature and to release a fourth gear. Various detection signals input through the input interface circuit 21 are converted to digital signals through an A/D converter 22, and then fed to a CPU 24. A program for executing a predetermined calculation of the CPU 24 is stored in a memory 24a associated with the CPU 24. A vehicle speed detection signal from a vehicle speed sensor 13, an engine rotational speed detection signal from an ignition pulse generator 14, a shift range signal from an inhibitor switch 14, and a throttle full close state detection signal from an idle switch 16, an ABS signal from an ABS control unit 19a, a cruise control signal from a cruise control unit, and a brake switch signal from a brake switch 19 are input to an input interface circuit 23. The vehicle speed detection signal from the vehicle speed sensor 13 is used to control a gear shifting, lockup, line pressure and transfer. The engine rotational speed detection signal from the ignition pulse generator 14 is used to smoothly control the lockup operation and to prevent overrunning of an engine in a "1", "2" or "3" range. The shift range signal from the inhibitor switch 15 is used to determine the line pressure. The throttle full close state detection signal from the idle switch 16 is used to release a lockup clutch and to control the line pressure. An output of the CPU 24 is applied to an output interface circuit 25 for controlling ON/OFF of shift solenoids (1)31, (2)32, (3)33 and an output interface circuit 26 for controlling duty ratios of duty solenoids (A)34, (B)35 and (C)36. The shift solenoids (1)31, (2)32 control gear shifting, especially, its timing, thereby reducing a gear shifting shock. The shift solenoid (3)33 controls an overrunning clutch and a timing of shifting from a third gear to a second gear. The timing control reduces a shock at the time of shifting down the speed, and the overrunning clutch is operated at the time of decelerating, thereby effecting an engine brake. The duty solenoid (A)34 regulates the line pressure to an optimum pressure responsive to a driving state. The duty solenoid (B)35 smoothly engages or disengages the lockup clutch. The duty solenoid (C)36 regulates a hydraulic oil pressure of a transfer clutch to control the rear wheel drive force. An embodiment of the present invention will be explained in detail with reference to Figs. 2 to 6. Referring back to Fig. 1, showing a control system including a failure detecting system for a brake switch connected to an automatic transmission of a vehicle. The control system employs a brake signal from the brake switch as one of input signals to control the automatic transmission. A failure of the brake switch is detected when conditions to be described later are satisfied. When the failure is detected, a transmission control based on the brake signal is prohibited. However, a normal state is recovered when an OFF signal of the cruise control is detected after one of the conditions to be described later is satisfied. Control for a four-wheel drive transfer clutch in the automatic transmission (control at the time of operating ABS) is performed in response to the brake signal. The operation of the failure detecting system for the brake switch connected to the automatic transmission control system described above will be explained by referring to Figs. 2 - 4. Fig. 2 shows a flow to determined a case where a brake on signal is not detected which the vehicle speed is decelerated until a vehicle is stopped, and when this phenomenon is continuously repeated predetermined times. More specifically, when a detection signal from the vehicle speed sensor 13 is input to the CPU 24 through an input interface circuit 23, the vehicle speed is judged (in a step 1001). When the vehicle speed is, for example, faster than 30km/hr, a check flag is set (in a step 1002). On the contrary, in case where the vehicle speed is slower than 30km/hr, presence/absence of the check flag is judged (in a step 1003). If the check flag is not set, the check flag is reset. In case where the check flag is set, ON/OFF of the brake switch 19 is judged (in a step 1004). If the brake switch 19 is judged to be turned on, the check flag is cleared, and a counter is also cleared (in a step 1005). In case where the brake switch 19 is turned off, whether or not the vehicle speed becomes "zero" is judged (in a step 1006). If it is judged that the vehicle speed becomes "zero", the check flag is cleared, and a counter is counted up (in a step 1007). In case where a counted-up value reaches a predetermined value N by repeating the count-up of the counter (in a step 1008), an error flag is set, and the automatic transmission at the time of brake is prohibited (in steps 1009 and 1010). Fig. 3 shows a flow to determine a case where the brake ON signal is not detected when a deceleration of the vehicle is larger than a predetermined value, and when this phenomena occurs continuously predetermined times. More specifically, whether the deceleration of the vehicle is larger than the predetermined value or not is judged (in a step 1101). In case where it is judged that the deceleration is larger than the predetermined value, presence/absence of the brake ON signal is judged (in a step 1102). If the brake ON signal is detected, a counter is cleared (in a step 1103). In case where the brake ON signal is not detected, the counter is counted up in a step 1104. When the counted-up value reaches a predetermined times, an error flag is set, and the automatic transmission control at the time of the brake is prohibited (in steps 1105 to 1107). Fig. 4 shows a flow combining both two cases described above. Whether the vehicle speed is faster than a predetermined value or not is judged prior to the decision of the deceleration shown in Fig. 3 (in a step 1201). Fig. 5 shows a flow to determine a case where absence of the brake ON signal is detected, predetermined times when the P or R range is selected in the vehicle having a shift locking mechanism. More specifically, when a shift range signal from the inhibitor switch 15 is input to the CPU 24 through the input interface circuit 23, a range position is judged (in a step 1301). In case where the range is altered from the P range to the R range, whether or not the brake switch 19 is turned on is judged (in a step 1302). That is, in this case, it is premise that the shift locking mechanism between the P and R ranges is provided, which is released by manipulating a shift lever with the depression of a brake pedal. In case where the brake ON signal is detected, stored information in a RAM(A) (not shown) of a memory 24a associated with the CPU 24 is cleared (in a step 2303). Moreover, in case where the brake ON signal is not detected, the number of counts stored in RAM(A), indicating the number of detections of the brake ON signal is added (in a step 1304). When the added number in the RAM(A) reaches a predetermined value N, a brake failure flag is set, and hence an automatic transmission control in response to the brake switch is prohibited (in a step 1313). Furthermore, in case where the added number in the RAM(A) (in a step 1305) does not reach the predetermined value N, the vehicle speed is judged (in a step 1306). That is, when a detection signal from the vehicle speed sensor 13 is input to the CPU 24 through an input interface circuit 23, a predetermined speed is compared with a detected speed from the vehicle speed sensor 13, and whether the detected speed is faster than the predetermined speed or not can be judged. In case where it is judged that the detected speed is larger than the predetermined speed, ON/OFF of the brake switch 19 is judged (in a step 1308). In case where the brake ON signal is detected, stored information in a RAM(B) (not shown) of the memory 24a is cleared, and further a brake failure flag is cleared (in steps 1309 and 1310). On the contrary, in case where the brake ON signal is not detected, the number of counts stored in RAM(B) indicating the number of detections of the brake ON signal is added to the RAM(B) (in a step 1311). When the added number in the RAM(B) reaches a predetermined value N, the brake failure flag is set, and hence the automatic transmission control in response to the brake switch is prohibited (in a step 1313). More specifically, summary of the flow detecting a failure of the brake signal is as follows. (1) When the vehicle speed is decelerated until a vehicle is stopped, a brake ON signal is not detected, and when this phenomenon occurs continuously predetermined times. (2) When a deceleration of the vehicle is larger than a predetermined value, the brake ON signal is not detected, and when this phenomenon occurs continuously predetermined times. (3) In case where the vehicle speed is larger than a certain value, and the condition (2) is satisfied, (4) In a vehicle having a shift locking mechanism, when a R range is selected from a P range, absence of the brake ON signal continuously occurs predetermined times. In case where any of the above conditions (1) to (4) is satisfied, a failure of the brake signal is detected, the automatic transmission control using the brake signal is prohibited. However, a normal state is recovered when the brake signal is detected after one of the above-described conditions is satisfied. Therefore, since the check switch for instructing a check before the cruise control like prior art is eliminated, its structure is not only simplified, but also a failure of the brake switch in the various running states is reliably detected, and hence the automatic transmission control using the brake signal is appropriately executed.

Claims: A failure detecting system for an automatic transmission of a vehicle employing a brake signal from a brake switch (19) as one of control signals to control said automatic transmission, the system comprising: vehicle speed detecting means (13) for detecting a vehicle speed; brake signal detecting means for detecting a brake signal when said brake switch (19) is turned on; and transmission control prohibiting means for prohibiting a transmission control, characterized in that said transmission control is based on said brake signal, when a number of times of how often said brake signal which ought to be detected has not been detected while said vehicle is decelerated from a predetermined speed to a zero speed reaches a predetermined number of times. The failure detecting system according to claim 1, wherein said transmission control prohibiting means are for prohibiting said transmission control based on said brake signal, when a deceleration rate of said vehicle obtained from said vehicle speed is detected by said vehicle speed detecting means (13), and when a number of times of how often said brake signal which ought to be detected has not been detected reaches a predetermined number of times. The failure detecting system according to claim 1, wherein said transmission control prohibiting means are for prohibiting said transmission control based on said brake signal, when said vehicle speed detected by said vehicle speed detecting means (13) is larger than a predetermined speed, when a deceleration rate of said vehicle obtained from said vehicle speed detected by said vehicle speed detecting means (13) is larger than a predetermined value, and when said brake signal which ought to be detected is not detected. A failure detecting system for an automatic transmission of a vehicle employing a brake signal from a brake switch (19) as one of control signals to control said automatic transmission, the system comprising: brake signal detecting means for detecting a brake signal when said brake switch (19) is turned on; transmission control prohibiting means for prohibiting a transmission control, characterized by shift signal generating means (15) for generating a shift signal so as to instruct an appropriate gear position to said automatic transmission, wherein said transmission control is based on said brake signal, when said shift signal from said shift signal generating means (15) indicates a change from a parking (P) range to a reverse (R) range, and when a number of times of how often said brake signal which ought to be detected has not been detected reaches a predetermined number of times. A method for detecting a failure of an automatic transmission for a vehicle employing a brake signal from a brake switch (19) as one of control signals to control said automatic transmission, comprising the steps of: detecting a vehicle speed; detecting a brake signal when said brake switch (19) is turned on; and prohibiting a transmission control, characterized in that said transmission control is based on said brake signal, when a number of times of how often said brake signal which ought to be detected has not been detected while said vehicle is decelerated from a predetermined speed to a zero speed reaches a predetermined number of times. The method for detecting a failure according to claim 5, wherein said transmission control based on said brake signal is prohibited, when a deceleration rate of said vehicle obtained from said vehicle speed is larger than a predetermined value, and when a number of times of how often said brake signal which ought to be detected has not been detected reaches a predetermined number of times. The method for detecting a failure according to claim 5, wherein said transmission control based on said brake signal is prohibited, when said vehicle speed is larger than a predetermined speed, when a deceleration rate of said vehicle obtained from said vehicle speed is larger than a predetermined value, and when said brake signal which ought to be detected is not detected. A method for detecting a failure of an automatic transmission for a vehicle employing a brake signal from a brake switch (19) as one of control signals to control said automatic transmission, comprising the steps of: detecting a brake signal when said brake switch (19) is turned on; prohibiting a transmission control, characterized by the further step of generating a shift signal so as to instruct an appropriate gear position to said automatic transmission, and wherein said transmission control is based on said brake signal, when said shift signal indicates a change from a parking (P) range to a reverse (R) range, and when a number of times of how often said brake signal which ought to be detected has not been detected reaches a predetermined number of times.

Inventors: SAKAKIYAMA RYUZO, SHIRAKAWA KIMINAGA, TEZUKA KAZUNARI, SAKAKIYAMA, RYUZO, SHIRAKAWA, KIMINAGA, TEZUKA, KAZUNARI
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F16H61
IPC codes: F16H61, F16H63, F16H59, B60T17, B60K31, B60W50